Ryoichi Morimoto

Mesoporous platinum with giant mesocages templated from lyotropic liquid crystals consisting of diblock copolymers

Templated synthesis of nanostructured metals with tunable composition, structure, and morphology allows us to finely control the metals properties, which is a typical example of materials nanoarchitectonics that emphasizes the importance of novel sizeand shape-dependent properties. Traditionally, various nanostructured metals (for example, nanowire arrays, bicontinuous nanowire networks, nanoparticle arrays) have been prepared by utilizing hard templates including mesoporous silica. Currently, lyotropic liquid crystals (LLCs), formed by assembling Cn(EO)m-type surfactants (EO = ethylene oxide), have been utilized as soft templates to directly prepare mesoporous metals with hexagonally packed cylindrical mesospace. In such LLCs, metal nanoparticles with almost uniform size are continuously deposited to form unique frameworks consisting of connected nanoparticles, which contribute to the development of novel metal-based nanomaterials that are not achievable by hard templating. Surprisingly, all the mesoporous metals prepared by the soft templating technique have been limited to 2D hexagonal mesostructures with mesopores less than 4 nm in diameter. Both the limits of mesostructures and pore size seriously devalue the advantages of mesoporous metals, because a small mesospace suppresses effective movement of guest species within the mesopores. Giant mesopores can incorporate large biological molecules, and also volume changes caused by incorporation of guest species into host matrices are effectively relaxed. Cage-type mesostructures should enhance the accessibility of various species. Therefore, to further explore the potential properties of nanoarchitectured metals, the versatile control of mesostructures and pore size is vital. Herein, we report the preparation of a new type of mesoporous Pt particle with giant mesocages connected closely in three dimensions, templated from LLCs consisting of diblock copolymers. The size of the mesocages is the largest (about 15 nm) reported in mesoporous metals. The advantage of diblock copolymers is that their high molecular weight and composition are well designed. By utilizing LLCs made of such designed block copolymers, new nanoarchitectured metals with various mesostructures and pore sizes should be realized. First, a precursor solution was prepared by mixing distilled water (0.75 g), hydrogen hexachloroplatinate(IV) hexahydrate (H2PtCl6·6H2O; 0.75 g), poly(styrene-b-ethylene oxide) block copolymer (PS3800-b-PEO4800, polydispersity index: 1.05; 0.25 g), and tetrahydrofuran (THF; 12.5 g) as volatile solvent (Figure 1a). Then, the precursor solution was drop-coated onto an indium tin oxide (ITO; surface resistivity 10 Wcm ) substrate. After the preferential evaporation of THF, a yellow LLC film was formed over the entire area of the substrate (Figure 1b). This LLC mesostructure before Pt deposition was proved by XRD measurement in the lowangle range (see the Supporting Information, Figure S2). An intense single peak (d 16 nm) was observable, which indicates that at least a periodic mesostructure was formed, although the dimensionality was not identified. For the

Surface chirality induced by rotational electrodeposition in magnetic fields

The surfaces of minerals could serve important catalytic roles in the prebiotic syntheses of organic molecules, such as amino acids. Thus, the surface chirality is responsible for the asymmetric syntheses of biomolecules. Here, we show induction of the surface chirality of copper metal film by electrodeposition via electrochemical cell rotation in magnetic fields. Such copper film electrodes exhibit chiral behaviour in the electrochemical reaction of alanine enantiomers, and the rotating direction allows control of the chiral sign. These findings are discussed in connection with the asymmetric influence of the system rotation on the magnetohydrodynamic micro-vortices around the electrode surfaces.

Lifetime of Ionic Vacancy Created in Redox Electrode Reaction Measured by Cyclotron MHD Electrode

The lifetimes of ionic vacancies created in ferricyanide-ferrocyanide redox reaction have been first measured by means of cyclotron magnetohydrodynamic electrode, which is composed of coaxial cylinders partly exposed as electrodes and placed vertically in an electrolytic solution under a vertical magnetic field, so that induced Lorentz force makes ionic vacancies circulate together with the solution along the circumferences. At low magnetic fields, due to low velocities, ionic vacancies once created become extinct on the way of returning, whereas at high magnetic fields, in enhanced velocities, they can come back to their initial birthplaces. Detecting the difference between these two states, we can measure the lifetime of ionic vacancy. As a result, the lifetimes of ionic vacancies created in the oxidation and reduction are the same, and the intrinsic lifetime is 1.25 s, and the formation time of nanobubble from the collision of ionic vacancies is 6.5 ms.

Magneto-Dendrite Effect: Copper Electrodeposition under High Magnetic Field

Ionic vacancy is a by-product in electrochemical reaction, composed of polarized free space of the order of 0.1 nm with a 1 s lifetime, and playing key roles in nano-electrochemical processes. However, its chemical nature has not yet been clarified. In copper electrodeposition under a high magnetic field of 15 T, using a new electrode system called cyclotron magnetohydrodynamic (MHD) electrode (CMHDE) composed of a pair of concentric cylindrical electrodes, we have found an extraordinary dendritic growth with a drastic positive potential shift from hydrogen-gas evolution potential. Dendritic deposition is characterized by the co-deposition of hydrogen molecule, but such a positive potential shift makes hydrogen-gas evolution impossible. However, in the high magnetic field, instead of flat deposit, remarkable dendritic growth emerged. By examining the chemical nature of ionic vacancy, it was concluded that ionic vacancy works on the dendrite formation with the extraordinary potential shift.

Origin of Nanobubbles Electrochemically Formed in a Magnetic Field: Ionic Vacancy Production in Electrode Reaction

As a process complementing conventional electrode reactions, ionic vacancy production in electrode reaction was theoretically examined; whether reaction is anodic or cathodic, based on the momentum conservation by Newton’s second law of motion, electron transfer necessarily leads to the emission of original embryo vacancies, and dielectric polarization endows to them the same electric charge as trans- ferred in the reaction. Then, the emitted embryo vacancies immediately receive the thermal relaxation of solution particles to develop steady-state vacancies. After the vacancy production, nanobubbles are created by the collision of the vacancies in a vertical magnetic field.